In the manufacturing industry, upon the basis of sales planning from the marketing points, there are planned a supply amount of materials and/or a production amount, as well as transportation means, being feasible under the restriction conditions upon the production capability and the term and amount of supply of materials. In recent years, the supply point of materials, the production point, the marketing point have been expanded not only domestically, but also abroad, and it is possible to select a plural number of the supply points, production points, and the marketing points, with regard to one kind or sort of the products. For example, regarding a product A, there may be a method, in which the materials are supplied from Asia so as to be fabricated in Japan, and another way in which they are supplied by Japan so as to be fabricated in the U.S.A., etc.
Several methods are proposed, in each of which the production plan forming the production mode is made up using a linear programming method. For example, in NIKKEI DIGITAL ENGINEERING (December of 1998), there is introduced a planning method for production plan, in which, under the restriction conditions of production capability and/or amounts of parts supply, while making a production time, a setup time, the maximum past due, and the maximum total past due as objective functions, the management indices, such as, the sales profit maximum, the average inventory minimum, observance of due date, effective operation, etc., are made minimal, respectively. Grade or rank of the each object is set in the priority, by giving weights thereon.
In case of using the management indices as objective functions, it is difficult to bring plural numbers of the management indices to the “minimum (or maximum)”, at the same time. For example, when setting the management index, “total past due” according to the conventional art at the minimum, due to the mechanism of the linear programming, the production plans are made up in an order of swiftness in their delivery times, regardless of the kinds thereof, therefore the setup time does not necessarily come to be a minimum. This is because those management indices have a relationship of so-called trade-off (negative correlation) between them. For the indices being in such the relationship as the trade-off, it is sufficient that both those values come to be values being desirable for a person in charge of planning the production plan, i.e., a person who can decides one's mind, but not be minimized (maximized) at the same time. The desirable value is a numeral value which can be given in advance, i.e., the “value” at which the target is set by the person in charge of planning the production plan, such as, “it is desired that the inventory should be at ¥100,000” or the like, or is a ranges in values, such as “it is desired that the inventory should be less than ¥200,000”. According to the conventional art, since parameters being changeable for approaching the management indices to those target values (or within the ranges) are only weights, therefore, for the purpose of approaching them to the target values, it is necessary to know the numeral values, at which the weights are to be set, by experiences. For the purpose of knowing them by experiences, it is necessary to solve a problem of the linear programming while adjusting the weights, as well as to repeat the operation of confirming the values of those management indices, therefore it sometimes necessitates times so as to make up the production plan.
When it is delayed in the planning of the production plan, the timings for starting the supply of materials, for preparation of production, and also for supplying the products onto the marketing points are delayed or postponed, it is impossible to deliver the products to the customers earlier than competitors.